1. Field of the Invention
The present invention relates in general to an implantable device for occipital fixing, and in particular to a device designed to fix a patient""s occipital bone to the end of a system for osteosynthesis of the spine and having longitudinal rods.
2. Description of the Prior Art
Rod systems for osteosynthesis of the spine are well known. They comprise two rods that are generally cylindrical and that are secured to respective sides of the vertebrae by means of screws and/or hooks.
Although such fixings are entirely suitable for securing the vertebrae, it is necessary to design special fixings when such a system needs to be extended to the skull, and more precisely to the occipital bone.
The present invention seeks to propose a device for anchoring in a bone wall of relatively small thickness and suitable for use in fixing rods of an osteosynthesis system for the spinal column to the occipital bone, which device provides satisfactory mechanical strength, while being simple to make and implement, and [minimizing] the need for holes to be made through said bone wall.
Thus, the present invention provides an implantable device for fixing a rod to a thin bone wall, in particular for fixing a rod of a system for osteosynthesis of the spine to the wall of the occipital bone of the skull, the device being characterized in that it comprises two parts each comprising both a body in which there is formed a passage for receiving the rod, and also a curved hook extending laterally relative to the body, in that each hook is of a shape such that the two hooks when placed face to face can be inserted simultaneously into an opening formed in said bone wall, the hooks being inserted by tilting the two parts in opposite directions so as to tend to move their bodies towards each other, the hooks moving away from each other behind said wall as said bodies move towards each other, and in that said passages of the two bodies come into alignment once the bodies have come close together, and the rod received therein is suitable for preventing said parts from tilting in the opposite direction.
Preferred but non-limiting features of the device of the invention are as follows:
the body of each part is generally oval in shape with at least one plane face, and said bodies are suitable for being placed essentially in contact with each other via their facing plane faces so as to ensure that both passages are in axial alignment;
each hook has a root region extending from the vicinity of said plane face, essentially at right angles relative to the axis of the passage, and an end portion extending substantially parallel to the axis of the passage;
the overall size of each hook as measured in a direction parallel to the axis of the corresponding passage is greater than the thickness of the body in said direction;
the body has a second plane face substantially parallel to the first plane face;
each hook is of a thickness that tapers progressively away from its root portion towards its free end;
each hook is of a width that is substantially constant over its entire extent;
each part includes means for locking the rod in its passage;
the locking means comprise a screw engaged in tapping formed in the body and opening out into the passage; and
the two parts are identical.